1. Field of the Invention
The present invention relates to semiconductor devices and their manufacture, and more specifically to a structure and method of making a semiconductor chip having a trench capacitor.
2. Description of the Related Art
One of the challenges of fabricating capacitors within the active device regions of semiconductor chips is to obtain sufficient capacitance while minimizing the area of the active semiconductor device layer occupied by the capacitor. One known way to reduce the semiconductor device area occupied by the capacitor is to use a trench capacitor. A trench capacitor has length extending in a vertically downward direction with respect to the semiconductor device layer, so that the long dimension of the trench capacitor extends out of the plane in which the semiconductor device layer extends.
A known way of increasing capacitance is to form the trench capacitor using a “bottle” process. In such process, first a relatively narrow trench is formed that extends through the active semiconductor device layer. Then, subsequent processing applied to a lower portion of the trench underlying the active semiconductor device layer to enlarge the lower portion of the trench, thus forming a capacitor having a larger surface area and capacitance.
Still further improvements in the fabrication and structure of a trench capacitor would be desirable.